The invention relates to a coupling for connecting hydraulic lines. The coupling includes a first coupling part containing a first valve which is inside a housing of the first coupling part. The first coupling part has means for receiving a second coupling part to which a second valve is added. The first valve has a valve body in the form of a truncated cone which, in its closed position, is in contact with a conical sealing surface of the housing of the first coupling part. The valve body is axially penetrated by an actuator, which is movable relative to it in the direction of the second valve. An actuator shaft is disposed transversely to the valve axis and penetrates the housing of the first coupling part. The actuating shaft acts upon the valve body of the first valve by means of actuating surfaces. The actuator is spring loaded by means of an opening spring supported at the valve body of the first valve in order to urge it toward the actuator surface.
A relevant coupling is described in DE 37 04 159 C2, issued Jun. 8, 1989. In this case, a very complicated eccentric shaft is provided, which, on the one hand, moves a sliding sleeve for the ball lock closure into the locking position, then moves an actuator, supported axially in a sleeve valve body, in the direction of the plug valve and opens it, and subsequently opens the sleeve valve body opposite to the direction of the actuator. Here, the face of the sleeve valve body directed toward the plug is constructed in such a manner that it has approximately the negative contour of the conical continuation of the plug valve extending from the plug. When connecting the plug, the conical continuation of the plug valve is directed beyond the plug receiving bore into the correspondingly shaped receptacle of the sleeve valve. Here the disadvantage is that the sleeve valve is opened and closed by means of forced guidance. The control surface of the eccentric shaft cooperates with two opposite surfaces at the valve body and a snap ring connected to it. By both, forced guidance of the valve body in both directions by way of the eccentric shaft is assured. Further, the eccentric shaft has separate control surfaces for operating the actuator in order to shift the plug valve into the open position. The operation of the actuator occurs at a time prior to the opening of the sleeve valve. The forced guidance has the effect of assuring secure closure of the sleeve valve only if the tolerances are well adhered to. The complicated eccentric shaft can, therefore, be produced only with great costs in order to maintain the required tolerances. Such a coupling is correspondingly expensive.
A further disadvantage consists in the fact that in order to assure that the sleeve valve cannot be opened when there is no plug in the coupling sleeve, considerable construction cost must be incurred in order to block the push sleeve in the open position. This is intended to assure that the eccentric shaft cannot be operated.
A further disadvantage is caused by the fact that such a coupling cannot be configured as a quick disconnect coupling. A quick disconnect coupling is of the type, if by application of a pulling force at one of the two connection points, the plug can be pulled out of the coupling sleeve without leakage of fluid from the hydraulic lines. The same applies in the case of an unintended loosening of the slide sleeve.
Quick disconnect couplings are easier to manipulate than couplings with sliding sleeves requiring the use of both hands where the sliding sleeve must be actuated by hand in order to initiate the loosening process. An advantage of the known coupling can be seen in the fact that, because of its shape, leakage during the coupling process can be kept relatively small because the surfaces of the oppositely located parts of the plug valve and the sleeve valve have narrow gaps between one another.
A further disadvantage is caused by the fact that the design requires a relative large actuation path, which amounts to approximately 180.degree.. During the installation of the coupling, this path must be regarded as a clearance space. The coupling, therefore, requires a relatively large space for its installation.
In the case of couplings of the aforementioned type, coupling under pressure is possible since the plug valve and the sleeve valve are opened only after a completed coupling process. This is particularly important because, for example, in the area of agriculture, ever stronger implements are employed which, even after they are uncoupled, retain a counter pressure or make it necessary to maintain it. In order to utilize the many opportunities of modern hydraulics optimally, a coupling is required which can close the lines under pressure without any problems. A further requirement consists in the fact that the amount of oil leakage occurring during uncoupling must be kept as low as possible. In the case of most couplings currently in use, the amount of leakage is up to 3 cm. The same amount of air frequently enters the hydraulic system during the uncoupling process, and this has a very damaging effect on the life expectancy of valves and seals.
DE 28 23 877 B2, discloses a coupling for connecting pipe lines where the valve, belonging to the first coupling part, has a valve body which can be moved by a cam, mounted on an actuating shaft, into the open or closed position by rotating the actuating shaft. The valve body pushes, while it moves into the open position, the valve body of the second coupling part into the open position. The actuating shaft is constructed in one piece and enclosed, for part of its length, by a sleeve. This coupling is intended to connect fluid lines of tank systems and tank vehicles. It can only be used in systems where the flowing liquid is under low pressure. It is not suited for hydraulic lines because the design, consisting of the actuator shaft and the sleeve, would be blown apart because the pressure acting upon the interior faces of the sleeve and actuator shaft cannot be neutralized. The contemplated radially directed locking screws cannot withstand the pressure. Further, it is not possible to design such a coupling as a quick disconnect coupling, where the valves of both coupling parts close automatically when the coupling is disconnected, even though the actuator shaft has not been operated.
Besides the known couplings described above, which include a conical valve body, quick connect couplings are also known, in which two ball valves located behind one another on a coupling sleeve are controlled by an actuator shaft (U.S. Pat No. 3,680,591). If the actuator shaft is turned to its open position, then the sleeve valve as well as the plug valve are opened. By the forced opening a back flow protection is also provided. It is known that back flows can effect undesired closing in the case of valves which are only spring-loaded. It is a disadvantage of this coupling that, during coupling of a plug under pressure, a space in the sleeve valve exposed to pressure must be first connected to a discharge line by a corresponding positioning of the eccentric shaft, if a pressurized medium is enclosed in this space. In this case, the pressurized medium is either released as leakage or it must be allowed to flow back to the tank through a special line. Also in the case of the uncoupling process a major leak occurs because the second valve, which is also adjacent to the plug valve of the coupling sleeve, closes only after some delay so that the oil in the enclosed space can still escape before the valve is finally placed in the closed position. The use of ball valves is disadvantageous because they rely on a metal-to-metal seal and they are only absolutely tight when the seal sets are made very precisely. Especially when only a low hydraulic pressure applies a force to these valve seats, they tend toward leakages, and they tend to be dirty due to the oil leaks and the associated contamination of the environment because dust and dirt are deposited on the oil film.
For this reason, the couplings using conical valve bodies are more favorable because better sealing conditions can be achieved. Valves with conical sealing surfaces allow the installation of soft seals, which further improve the already better sealing capability of the conical seating surfaces.